In routine practice of Radiotherapy (RT), the subject is positioned relative to the stationary center of the rotating arc carrying the RT source. Positioning implies both height and lateral adjustment of the subject table. This positioning is required to optimize the dose in the lesion beyond variation that can be obtained by applying RT rays from different angles.
Integration of MR (Magnetic Resonance) and Linear Accelerators (LINAC) opens new horizons in Radiotherapy by improved lesion targeting, especially for moving organs. In a practical implementation proposal, the LINAC rotates around the subject to hit the gross target volume (GTV) and clinical target volume (CTV) from multiple angles while minimizing the radiation exposure for surrounding tissues.
The combination of magnetic resonance apparatuses and LINAC radiotherapy sources is known. Typically a LINAC source is placed on a rotating gantry about the magnet and the magnet designed such that the LINAC rotates in a zero-field region of the magnet.
International patent application WO 2009/012577 A1 discloses the use of portal imaging to modify treatment parameters during radiotherapy.